This invention relates to stabilization of 3-isothiazolones microbicides. In particular, this invention relates to the stabilization of dilute solutions of 3-isothiazolone microbicides having very low levels of copper ion.
Microbicides are used commercially to prevent the growth of microbes in a variety of loci, such as cooling towers, metal working fluid systems, paint and cosmetics. One of the more important classes of microbicides is 3-isothiazolones. Many 3-isothiazolones have achieved commercial success because they are very effective in preventing microbial growth under a wide variety of conditions and in a variety of loci. Among the most important 3-isothiazolones are 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone, and mixtures thereof.
Although 3-isothiazolones are highly effective microbicides, some 3-isothiazolones suffer from being unstable under certain conditions. Without the presence of a stabilizer, many 3-isothiazolones chemically degrade and lose microbicidal efficacy. Much research has been devoted to stabilizing 3-isothiazolones.
Typical 3-isothiazolone products of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain between 1 and 25 percent by weight of the 3-isothiazolone mixture and a similar amount of a stabilizer. Concentrate compositions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone generally contain about 5 to 35 percent by weight of the 3-isothiazolone compounds and require about 10 to 25 percent by weight of a stabilizer. Dilute solutions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain about 0.5 to 5 percent by weight of the 3-isothiazolone compounds. Dilute solutions have different stabilization requirements from 3-isothiazolone concentrates.
A variety of stabilizers for 3-isothiazolone dilute solutions are known. These known stabilized 3-isothiazolone dilute solutions suffer from having a high metal salt content so as to cause coagulation of latexes under certain conditions or from having limited stability. For example, U.S. Pat. No. 5,461,150 (Gironda, et al.), herein incorporated by reference, discloses the stabilization of dilute solutions of 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone and mixtures thereof with a low level of cupric ion in the form of a copper salt other than nitrate or nitrite. The weight ratio of the copper ion to the 3-isothiazolone compounds is in the range of 0.02:1.5 to 0.0008:1.5. These stabilized dilute solutions show good short term stability (4 weeks at 55.degree. C., for example) but show no or limited long term stability (8 weeks at 55.degree. C., for example). This patent does not address the problem of precipitate formation upon storage of the 3-isothiazolone compositions.
Although the use of stabilizers enables 3-isothiazolone dilute solutions to retain their microbicidal efficacy for a period of time, other problems may develop without significant loss of 3-isothiazolones, such as the formation of precipitate upon storage. The presence of this precipitate does not impact the efficacy of the 3-isothiazolones; however, the presence of the precipitate gives undesirable appearance to users of the product. It is clearly preferable from a commercial standpoint to have a product which does not form a precipitate.
Thus, there is a continuing need for 3-isothiazolone dilute solutions that have good long term stability and that are free of precipitate.